Replace the use of marked with remark for doc/json generation
Summary: over time the node.js build process has outgrown marked and it's regular expression based processing model. See:
https://github.com/nodejs/node/pull/21081#issuecomment-399155282 https://github.com/nodejs/node/pull/21081#issuecomment-399197585 https://github.com/nodejs/node/pull/21081#issuecomment-399510285
It is time to replace it with something that involves a proper syntax tree which can be programmatically manipulated and from which artifacts like JSON can be confidently generated.